1. Field of the Invention
The present invention relates to a secondary sealed battery which can prevent overheating and short circuit at a roll center of a rolled electrode assembly by forming a mandrel along a central axis of the battery.
2. Description of the Related Art
Generally, a sealed battery has the drawback that it may explode when internal pressure is increased above an allowable level as a result of overcharging or abnormal operation thereof.
An electrode assembly typically comprises positive and negative electrode strips and a porous separator strip disposed between the positive and negative electrodes and rolled together.
The porous separator is designed, so that when an internal temperature of the battery is increased above an allowable level, to interrupt ion movement between the positive and negative electrodes by blocking the holes thereof, thereby preventing further electrochemical reaction to enhance the safety of the battery.
However, in the conventional sealed battery, since the rolled electrode assembly is highly heated at its center, particularly in the vicinity of an electrode tap attached to an innermost turn of a base substrate of the positive electrode, a center portion of the separator may lose its insulating function, causing a short circuit between the tap and a base plate of the negative electrode.
As a result, an electrochemical reaction between the positive and negative electrodes quickly occurs, causing a chemical melt down reaction such as decompositions of negative active material, electrolyte, and positive active material. This may be a fatal problem such as the explosion of the battery.
Therefore, the present invention has been made in an effort to solve the above described problems.
It is an objective of the present invention to provide a sealed battery which can prevent overheating and short circuiting at a roll center of a rolled electrode assembly by forming a mandrel along a central axis of the battery.
To achieve the above objective, the present invention provides a sealed battery comprising a can having a top opening; a rolled electrode assembly inserted into the can, the rolled electrode assembly having first and second electrodes and a porous separator disposed between the first and second electrodes, the first electrodes having a first base plate and a first active material deposited on the first base plate, and the second electrode having a second base plate and a second active material deposited on the second base plate; a cap assembly for sealing the top opening of the can; and a central turns disposed around an imaginary central axis of the rolled electrode assembly to support the rolled electrode assembly, the central turns being formed by at least 1.5 turns of one of the first and second base plates and the porous separator.
The sealed battery may further comprise an electrode tap connecting an innermost turn of the central turns to the cap assembly.
Preferably, the central turns are formed by at least 1.5 turns of the first base plate which is a positive base plate.
Turns of the second base plate starts at a point away from a point, where the tap is attached on the inner most turn of the first base plate, by 90-270xc2x0. The second base plate comprises an outermost turn contacting directly the can.
Preferably, the central turns are formed of less than 4 turns. The first electrode is a positive electrode, and the second electrode is a negative electrode.